Chapter 4 – Control Circuits

Publisher Summary This chapter explores various forms of controllers available from semiconductor manufacturers. The simplest form of a control circuit is variable frequency/constant on-time or pulse frequency modulation (PFM). The basic circuit of a current mode pulse width modulation (PWM) controller in a boost converter has two control loops. The outer loop measures the output voltage and provides an error signal to the inner loop. The inner loop compares the error signal and an analog of the inductor current to decide when to turn off the switch. The effect is to change the pulse width. The operation of the current mode controller has several advantages over a voltage mode controller. One of them is that the inductor current is a direct function of the error voltage, so for small signal analysis, the inductor can be replaced by a voltage controlled current source. This removes one order from the transfer function.